Carcinoma of the prostate gland is the most commonly diagnosed cancer and is the second leading cause of cancer death in US males. Over the last decade major advances in screening and treatment have lead to diagnosis at an earlier stage of disease. However, not all men are cured by primary treatment, and many men require secondary androgen suppression therapy. Whether this therapy will increase metastasis-free progression and decrease cancer-specific death rates remains to be determined. However, a known consequence of long-term therapy with hormonal suppression is bone loss with an increased risk of osteoporotic fractures. This study addresses this potential adverse effect of hormonal suppression therapy and its prevention. The aim of this proposal is two-fold. In a short-term study, we will examine the relation between markers of bone turnover and early changes in hormone levels in men receiving LHRH therapy prior to definitive treatment for locally advanced prostate cancer. Treatment of half the subjects with oral 17-b micronized estradiol will be used to determine if the effects of hormonal suppression therapy on serum and urine markers of bone turnover can be reversed by estrogen. In a long-term study we will look at the effect on bone mass of LHRH treatment over 1 year in men with locally advanced prostate cancer who have failed primary therapy. Half of the group will be randomized to oral 17-b micronized estradiol to determine if bone mass can be preserved by this therapy. This study will not only test the effects of hormonal suppression on the skeleton, but also evaluate a preventive approach using low dose estrogen.